The present invention relates to a composition for forming a protective layer of a dielectric material which is suitable for forming a dielectric material-protective layer containing an alkaline earth metal oxide, more specifically it relates to a composition for forming a protective layer of a dielectric material which comprises alkaline earth metal oxide particles and, as a binder precursor, an organic compound containing a specific metal in a molecule thereof, which provides an excellent protective effect.
In a display device using electron rays such as a vacuum fluorescent display (VFD) and a gas discharge panel (or a plasma display panel), a coating layer comprising an alkaline earth metal oxide which is formed on the surface of a dielectric material has conventionally been used as a dielectric material-protective layer. Particularly in a gas discharge panel, an electrode for discharge is covered with a dielectric material such as a glass, for example, a lead borosilicate glass, and therefore, if discharge is carried out on the surface of the dielectric material, it causes damage to the dielectric material, due to corona discharging. Accordingly, a protective layer has been provided on the surface of the dielectric material. Magnesium oxide and others are used as the protective layer of such a dielectric material, and a vacuum evaporation coating method is employed for formation of the protective layer.
However, if a gas discharge panel having a large picture such as a High-Definition television (HDTV) set is produced by the vacuum evaporation coating method, a large sized vacuum evaporation coating device accompanied by a large scale apparatus for maintaining the vacuum is required, which is not practical for industrial purposes.
For the above reasons, it has been tried to form a protective layer on the surface of the dielectric material by printing and firing. For example, Uchiike et al. prepared a sample of AC plasma display by a thick film technique using a paste containing magnesium oxide powder or magnesium hydroxide powder and evaluated it (refer to Material 4-3 of the Annual Meeting of the Television Association, p 71 (1991); and Material 5-1 of the Annual Meeting of the Television Association, p 101 (1992)), but failed to provide sufficient functions.
As an uneven thickness of such a dielectric material-protective layer causes an uneven emission, a protective layer having a homogeneous film thickness is required. Also, if the layer has pinholes or cracks, lead or other material can precipitate from the glass which is used as the dielectric material. Accordingly, the protective layer must not have such defects.
The present inventors obtained a dielectric material-protective layer which has a homogeneous film thickness without defects by coating a surface of a dielectric material with an alkoxide or an organic acid salt which contains an alkaline earth metal such as magnesium in a molecule thereof and firing the same (Japanese Patent Application No. 308525/1992). The present inventors also obtained a dielectric material-protective layer which has a homogeneous film thickness without defects by using a coating composition in which alkaline earth metal oxide particles are combined with the similar organic compound as mentioned above as a binder precursor (Japanese Patent Application No. 12702/1993). These dielectric material protective layers each have the advantage that they are excellent in sputtering-resistance and can be formed without heating at high temperatures or without using a large sized apparatus. However, the alkaline earth metal-containing organic compound to be used is easily hydrolyzed so that attentions should be paid when using it, depending on the purposes. For the above reason, a dielectric material-protective layer employing a binder precursor which can be easily handled has been desired.